1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine arranged such that a power switch for intermittently feeding a primary current to an ignition coil and a primary coil and a secondary coil of the ignition coil are contained in an insulation case, and the power switch, the primary coil and the secondary coil are fixed by an insulating resin material poured into the insulation case.
2. Description of the Related Art
FIG. 5 is an overall perspective view of a conventional ignition apparatus for internal combustion engine disclosed in Japanese Utility Model Laid-Open No. 4-77220, FIG. 6 is a longitudinal cross sectional view of FIG. 5, FIG. 7 is a perspective view of an insulation case of FIG. 5 and FIG. 8 is a an electric circuit diagram of the ignition apparatus for internal combustion engine. In the drawings, a hole 1b is defined to the bottom of the accommodating unit 1a of a synthetic resin insulation case 1 at the center thereof. The central portion of a first E-shaped iron core 2 of an ignition coil passes through the hole 1b. A second E-shaped iron core 3 of the ignition coil is spaced apart from the first E-shaped iron core 2-in confrontation therewith. A primary coil 5 is wound through a bobbin 4 around the central portion of the first E-shaped iron core 2 and the central portion of the second E-shaped iron core 3 spaced apart from the first E-shaped iron core 2 in confrontation therewith. The ignition coil has a secondary coil 6 wound around the outer periphery of the primary coil 5 thereof.
A power switch 7 is accommodated in an auxiliary accommodating section 1c projecting from the accommodating section 1a. The power switch 7 includes a tray-shaped copper heat sink 8, a power transistor 9 accommodated in the heat sink 8, a hybrid integrated circuit (hybrid IC) 10 for driving and controlling the power transistor 9, a silicone gel 11 filled into the heat sink 8 for protecting the power transistor 9 and the hybrid integrated circuit 10 and a rid 12 for sealing the interior of the heat sink 8.
The insulation case 1 includes a holding section 1d for a high-tension terminal 13 as a high-tension portion of the ignition coil and a holding section 1e for a low-tension terminal unit 14. The low-tension terminal unit 14 includes a VB terminal 14a (FIG. 8) for connecting the primary coil 5 to the battery of an automobile, an ignition signal input terminal 14b (FIG. 8) for imposing an ignition signal from a control unit (not shown) to the power switch 7 and a ground terminal 14c. Note, the accommodating section 1a and auxiliary accommodating section 1c of the insulation case 1 are filled with an insulating resin material 15 composed of a cured epoxy resin.
In the ignition apparatus for the internal combustion engine arranged as described above, a primary current flowing to the primary coil 5 of the ignition coil is controlled through the power switch 7 in response to an ignition signal which is input from the ignition signal input terminal 14b through the control unit. A high-tension voltage is generated to the secondary coil 6 of the ignition coil in accordance with the primary current flowing to the primary coil 5.
In this example, the heat sink 8 is used to secure the heat radiation property of the power switch 7 so as to uniformly diffuse heat from the powerswitch 7 to the overall heat sink 8 and discharge the heat to the outside air through the insulating resin material 15 and the insulation case 1.
Since the power transistor 9 has a collector directly attached to the heat sink 8 in the conventional ignition apparatus for the internal combustion engine, there is a problem that high-tension voltage generated at the secondary coil 6 induces a voltage at the heat sink 8 and the power transistor 9 causes malfunction. Further, there is also a problem that due to a high-tension voltage induced to the heat sink 8, noise is superposed on an ignition signal in an ignition signal input line through a capacitance C between the collector and the base of the power transistor 9, thereby causing malfunctions of other equipment.